AP Photo/Ric Francis

A truck passes through a radiation portal monitor Wednesday, July 20, 2005, at the Port of Los Angeles. U.S. Customs and Border Protection commissioner Robert C. Bonner visited the area Wednesday and gave a briefing on homeland security measures.

LOS ANGELES (AP) - The head of the U.S Border Patrol unveiled radiation detectors to scan incoming ocean cargo for nuclear weapons and dirty bombs, a measure he says will not choke the flow of trade at the nation's busiest port complex.

Customs and Border Protection Commissioner Robert C. Bonner said the 20-foot-(six-meter-) high devices would substantially boost port security at the Los Angeles-Long Beach harbor complex without causing major delays.

"We have to save American lives, but we also have to do it in a way ... that preserves American livelihoods," Bonner said during a visit Wednesday to the ports of Long Beach and Los Angeles.

The dual ports handle more than 40 percent of all cargo shipped into this country, and 80 percent of the imports from Asian manufacturing countries such as China and India.

The federal government has installed about 14 of the monitors, with plans to install a total of 90 by year's end.

Trucks carrying cargo unloaded from ships will pass through the systems, a process that takes a matter of seconds.

If the machines find signs of radiation, the container will get another scan and possibly an inspection by hand-held devices to help identify how much and what kind of radiation is present. That secondary inspection can last 10 minutes or longer.